A conventional MOS-based charge coupled device (CCD) (see, W. S. Boyle and G. E. Smith, Bell Syst. Tech. J. 49, 587, 1970) utilizes a MOS structure with a single semiconductor material—silicon, to absorb light, store the photogenerated charges, and read out the stored charges laterally. As is schematically illustrated in FIG. 1, a large external voltage is typically required to form a charge-storage channel at the semiconductor/oxide interface and to deplete the silicon deeply to enhance near-infrared (NIR) response. Such conventional CCD design, however, is not operationally effective when constructed with mid-wave and long-wave IR materials. Narrow-gap semiconductors have high band-to-band tunneling current and high generation-recombination (G-R) current under deep-depletion condition, which induce high noise and short charge storage time. In addition, a MOS capacitor using a narrow-gap semiconductor has a limited charge capacity because of its low background potential and charge trapping problem when shifting the charges laterally. (see, A. Rogalski, Progress in Quantum Electronics 36, 342-473, 2012) Although efforts have been made to develop monolithic FPAs using narrow-gap semiconductors such as HgCdTe and InSb, (see, M. V. Wadsworth, et. al. IEEE Transactions on Electron Devices 42, 2, 1995; and R. D. Thom, et. al. IEEE Transactions on Electron Devices ED-27, 1, 1980) silicon-based monolithic FPA technology appears to remain is the only mature technology with respect to fabrication yield and attainment of near-theoretical sensitivity. (see. A. Rogalski, Progress in Quantum Electronics 36, 342-473, 2012) In comparison with the commercial CMOS-based imaging technology, power consumption of the CCD is much higher, and a typical portable camera that utilizes a CCD imager has a much shorter battery lifetime than that utilizing a CMOS imager.
Developments to improve the process of fabrication and the operational advantages of the CCDs while maintaining the already-achieved features (such as, for example, noise suppression, high sensitivity, high fill factor) continue.